[Paper Review] Noncoherent Multiantenna Receivers for Cognitive Backscatter System with Multiple RF Sources

Huayan Guo, Qianqian Zhang+2 more|arXiv (Cornell University)|Aug 13, 2018

Energy Harvesting in Wireless Networks30 references10 citations

TL;DR

This paper proposes noncoherent multiantenna receivers for cognitive backscatter systems with multiple RF sources, enabling high-throughput transmission without pilot signals or channel state information. By leveraging maximum likelihood detection and a blind clustering-based channel estimation method, the system achieves reliable performance even under strong interference, with throughput increasing when receive antennas exceed the number of RF sources (M > K).

ABSTRACT

Cognitive backscattering, an integration of cognitive radio and backsatter modulation, is emerging as a potential candidate for green Internet of Things (IoT). In cognitive backscatter systems, the backscatter device (BD) shares not only the same spectrum, but also the same radio-frequency (RF) source with the legacy system. In this paper, we investigate the signal transmission problem, in which a basic transmission model is considered which consists of K RF sources, one BD and one reader equipped with M antennas. A non-cooperative scenario is considered, where there is no cooperation between the legacy systems and the backscatter system, and no pilots are transmitted from the RF sources or BD to the reader. The on-off keying differential modulation is adopted to achieve noncoherent transmission. Firstly, through the capacity analyses, we point out that high-throughput backscatter transmission can be achieved when the number of the receive antennas satisfies M>K. The Chernoff Information (CI) is also derived to predict the detection performance. Next, we address the signal detection problem at the reader. The optimal soft decision (SD) and suboptimal hard decision (HD) detectors are designed based on the maximum likelihood criterion. To tackle the non-cooperation challenge, a fully blind channel estimation method is proposed to learn the detection-required parameters based on clustering. Extensive numerical results verify the effectiveness of the proposed detectors and the channel estimation method. In addition, it is illustrated that the increase of K may not necessarily lead to performance degradation when multiple receive antennas are exploited.

Motivation & Objective

• Address the challenge of reliable backscatter signal detection in cognitive backscatter systems where multiple legacy RF sources transmit modulated signals, creating strong, unknown direct-link interference (DLI).
• Overcome the limitations of conventional noncoherent energy detectors, which suffer from an error floor that prevents performance improvement with increased RF transmit power.
• Design a receiver architecture that enables high spectral efficiency and reliable communication in noncooperative, blind scenarios with no pilot signals or channel state information.
• Enable high-throughput backscatter transmission by exploiting spatial diversity through multiple receive antennas, particularly when M > K.

Proposed method

• Formulates a noncoherent transmission model using on-off keying (OOK) differential modulation to avoid the need for channel estimation at the backscatter device.
• Derives the Chernoff Information (CI) to predict detection performance and establish theoretical limits on error probability.
• Designs optimal soft decision (SD) and suboptimal hard decision (HD) detectors based on the maximum likelihood criterion to improve detection accuracy.
• Proposes a fully blind channel estimation method using clustering to estimate the required detection parameters without prior knowledge of the RF sources or channel states.
• Utilizes Monte Carlo integration to numerically compute the average achievable rate for on-off modulated signals, accounting for random channel fading and interference.
• Analyzes the system capacity and shows that throughput can grow without bound when M > K, indicating that increasing receive antennas can counteract interference from multiple RF sources.

Experimental results

Research questions

• RQ1 Can high-throughput backscatter communication be achieved in a noncoherent, noncooperative system with multiple RF sources and no pilot signals?
• RQ2 How does the number of receive antennas (M) affect the system's capacity and error performance when multiple RF sources (K) are present?
• RQ3 Can blind channel estimation based on clustering effectively recover the parameters needed for reliable detection in the absence of channel state information?
• RQ4 Does increasing the number of RF sources (K) necessarily degrade system performance when multiple receive antennas are employed?
• RQ5 What is the theoretical limit on the achievable rate for on-off modulated backscatter signals in the presence of unknown, modulated direct-link interference?

Key findings

• High-throughput backscatter transmission is achievable when the number of receive antennas exceeds the number of RF sources (M > K), as capacity grows without bound under ideal conditions.
• The Chernoff Information (CI) provides a reliable metric for predicting detection performance and characterizing error probability in the presence of unknown interference.
• The proposed optimal soft decision (SD) and suboptimal hard decision (HD) detectors based on maximum likelihood criterion significantly outperform conventional energy detectors, especially in high-SNR regimes.
• The blind clustering-based channel estimation method successfully recovers detection parameters without prior knowledge of the RF sources or channel states, enabling reliable operation in noncooperative environments.
• Numerical results confirm that increasing K does not necessarily lead to performance degradation when M > K, demonstrating the robustness of multiantenna diversity in interference-limited scenarios.
• The average achievable rate for on-off modulated signals is computed via Monte Carlo integration, showing that the system can sustain high spectral efficiency even under fading and interference.